This invention relates to a process and system for rearing shrimp and, in particular, to a process and system for rearing shrimp to the post-larvae stage on a commercial scale under controlled conditions.
In recent years, there has been considerable interest in the development of techniques for rearing or cultivating shrimp in artificial or indoor environments under controlled conditions. Techniques of this type can be viewed as falling into two types of systems and processes directed to the growing of shrimp before and after they have reached the larvae stage. The former type systems and processes primarily concern the rearing stages of mating of adult shrimp, spawning of shrimp eggs by the gravid female, hatching of the spawned eggs, and the cultivation of the hatched baby shrimp to the post-larvae stage. More particularly, these systems and processes have attempted to control the environmental conditions, such as, for example, lighting, temperature, and water make-up, so as to provide conditions which promote the aforementioned rearing stages year round. However, while successful in this regard to some degree, they have often employed cumbersome procedures requiring significant amounts of time. As a result, they have not proved entirely suitable for commercial production.
For example, in these systems it is often the case that the stages of mating, spawning, hatching and cultivating require the movement of the adult shrimp to and from various tanks, which is a time consuming process. Thus, females, once they are gravid, are often moved from their mating or brood tank to a spawning tank where they drop their eggs. Likewise, the females, after spawning, are again moved from the spawning tank prior to the hatching process. Movement of the adult shrimp from the brood tank is also often carried out to permit drainage and subsequent refilling of the tank.
U.S. Pat. No. 3,473,509 discloses one such controlled type process in which after mating and spawning, the adult shrimp are removed from the tank prior to hatching. U.S. Pat. No. 3,682,138 discloses another of these processes. In this case, each adult female shrimp is isolated from a male shrimp, until the female shrimp has molted and is ready to mate. At this time, the barrier between the shrimp is removed and mating occurs. Subsequent thereto, the female is removed from the tank to a further facility where hatching is to take place. Further patent references disclosing similar movement of a gravid female to a separate hatching tank are as follows: U.S. Pat. Nos. 3,685,489; 3,696,788; 3,540,414. Additionally, this type of movement of a gravid female is disclosed in C.C. Dugan, W. Hagood, Thomas A. Franks, "Development of Spawning and Mass Larvae Rearing Techniques for Brackish-Freshwater Shrimps of the Genus Macrobrachium (Decopoda Palaemonidae), "Florida Marine Publications, No. 12 (October 1975). The latter publication further discloses a collection system for collecting the shrimp after hatching by trapping them in collectors placed in the water flow passing from the hatching tank.
As can be appreciated, the above movement of the adult shrimp from one tank to another is time consuming and not entirely satisfactory where commercial production of shrimp is sought.
It is thus an object of the present invention to provide a process and apparatus for cultivation of shrimp to the larvae stage which is more efficient and, hence, geared to commercial production.
In systems of the above type, once hatching has occurred, the resultant baby shrimp are placed in so-called larvae tanks where they are kept until they mature through the larvae stage. The larvae tanks provided to date, however, have suffered from a variety of problems all of which have contributed to larvae mortality. One tank construction which has had some degree of success includes an upper cylindrical tank portion and a lower or bottom conical tank portion. This type of construction facilitates suspension of the larvae and larvae food, thereby preventing the accumulation of bottom debris. However, the sharp conical taper of the bottom tank portion causes pile up of larvae who descend during molting, thereby increasing larvae mortality.
It is, therefore, a further object of the present invention to provide a method and apparatus for growing shrimp through the larvae stage which is provided with an improved larvae rearing tank structure.